Studies will be performed to delineate the precise physiological and biochemical mechanisms involved in the hepatic disposition of the biliary radiographic contrast materials. This is an extension of previous work performed in this laboratory using the biliary contrast materials as tools to achieve a more complete understanding of basic hepatobiliary biology and pathophysiology. The work is a systematic study of the uptake, conjugation and biliary excretion of contrast materials using isolated hepatocytes in primary culture and in vivo rat preparations. The hepatic disposition of the parent compounds and their hepatic metabolites by livers from normal, aged and Gunn rats will be analyzed.